Area of the end faces = 2 × 3 × 22 = 24 sq.m[Area of end faces = 2 πr2.]

Total surface area = 24 + 24 = 48 sq.m[Substitute in step2.]

Rate of painting = $10 per sq.m
[Given.]

Cost of painting = 10 × 48 = $480[Substitute in step1 and simplify.]

Correct answer : (4)

6.

A cylindrical open vessel is to be made of a thin sheet of uniform thickness. If the diameter of the vessel is 30 cm and the height is 22 cm, then find the area of the sheet required to make it. [Take π = 3.]

a.

2778 cm2

b.

2582 cm2

c.

2753 cm2

d.

2655 cm2

Solution:

Area of the sheet = Curved surface area of the cylinder + Base area of the vessel.[Analysis.]

Radius of the vessel = d / 2 = 15 cm[Given.]

Height of the vessel = 22 cm
[Given.]

Curved surface area = 2πrh = 2 × 3 × 15 × 22 = 1980 sq.cm[Formula.]

Area of the base = π × r2 = 3 × 152 = 675 sq.cm[Formula.]

Area of the sheet = 1980 + 675 = 2655 cm2[From steps 4 and 5.]

Correct answer : (4)

7.

The inner and outer diameter of a metallic pipe are 7 cm and 8 cm. Length of the pipe is 4 m. Find the total surface area of the pipe in sq.cm. [Take π = 3.]

a.

18022.50 sq.cm

b.

17946.50 sq.cm

c.

18089.50 sq.cm

d.

18198.50 sq.cm

Solution:

Total surface area of the pipe = Inner curved surface area + Outer curved surface area + Area of two end faces.[Formula.]